This invention relates to a method and apparatus for disinfecting water, and particularly to such an apparatus and method which employs coherent ultraviolet light generated by a laser the effect of which is enhanced by the dispersal of a gas in the liquid being treated.
In U.S. patent application Ser. No. 571,228, filed Jan. 16, 1984 for "Laser Disinfection of Fluids", and assigned to the assignee of this application, there is disclosed a method and apparatus for disinfecting a fluid such as water which involves passing a stream of the fluid through a laser beam which radiates coherent light in the ultraviolet range. The application particularly discloses methods and apparatus which use a gas pulsed laser whose rate of pulse may be adjusted and therefore whose intensity of light may also be adjusted. The gas pulsed laser is of the type which employs a spark gap switch as the means by which the pulsing of the gas pulsed laser is triggered.
The efficacy of the disinfection apparatus and process of the aforesaid application is enhanced by suspended particles in the water or other fluid being treated. Such particles have the effect of scattering the laser beam and making it more likely that any bacteria will be exposed to coherent ultraviolet light. The suspended particles do, however, afford a support for bacteria and may as a result shield the bacteria from exposure to the coherent ultraviolet light. One approach to solving that problem is to move the fluid at a relatively high velocity so that the suspended particles will be caused to tumble and all sides will be exposed.
There are occasions when the turbidity of the fluid is insufficient to provide the necessary suspended particles to cause the desired dispersal of the laser beam. There are other occasions when the fluid, although high in turbidity, cannot be moved at a sufficient velocity so as to cause the necessary tumbling to expose all sides of the suspended particles to the coherent ultraviolet light.
The spark gap switch in a gas pulsed laser generates a considerable amount of ozone during its operation. The ozone is damaging to the equipment and can be offensive to personnel. At the same time, ozone is a known disinfectant which can be advantageously utilized.
The present invention makes advantageous use of the ozone which is a by-product of the gas pulsed laser and at the same time enhances the laser disinfection of the water. By disinfection is meant the ability to kill bacteria primarily by direct contact rather than by secondary photochemical effect. Although the method and apparatus of this invention is particularly adapted for the treatment of water, it can also be employed to disinfect fluids generally, including those which are water based and those which are not, and including gases such as air.